Method for controlling the shifting sequence of a continuous automatic transmission, especially a motor vehicle, comprising gear step changeovers

ABSTRACT

The method serves for the shift sequence control of a continuous automatic transmission, especially of a motor vehicle, having gear-stage switchover. The transmission ratio of the automatic transmission is adjustable within a set gear stage by means of an adjusting unit. Here, it is provided that a coordinated, data-dependent control of the gear stage switchover and the continuous transmission ratio adjustment takes place with the aid of a common shift sequence control system.

[0001] The invention relates to a method for the shift sequence controlof a continuously variable automatic transmission, especially of a motorvehicle, having gear-stage switchover. The transmission ratio of theautomatic transmission is continuously adjustable within a set gearstage by means of an adjusting unit in accordance with the preamble ofclaim 1.

STATE OF THE ART

[0002] Continuous automatic transmissions having gear-stage switchoverare already known under the designation “CVT-transmission”. This relatesto combination transmissions for motor vehicles which have a steppedautomatic (planetary sets) and a continuously adjustable unit forcontinuously adjusting the transmission ratio within a particularadjusted gear stage (range).

[0003] The known methods for shift sequence control are unfortunatelynot suited to ensure a satisfactory adjustment of the transmission ratioon such a combination transmission (CVT-transmission having rangeswitchover).

ADVANTAGES OF THE INVENTION

[0004] The method of the invention is characterized in that acoordinated, data-dependent control of the gear stage switchover and thecontinuous transmission ratio adjustment takes place by means of acommon shift sequence control system. The control of the gear-stageswitchover as well as of the continuous transmission ratio adjustment iscoordinated within an adjusted gear stage (range) by means of a commonshift sequence control system. For this reason, it is possible toachieve adjustment actions of a transmission ratio on a continuouslyvariable automatic transmission flexibly by means of suitable datachanges. A coordinated, data-dependent control of this kind therebypermits a correct shift or adjustment of a transmission ratio on acorresponding continuous automatic transmission. This shift oradjustment of a transmission ratio is satisfactory with respect to theoperation of a vehicle. A corresponding control by means of ahigher-ranking shift sequence control system can be realized in arelatively simple manner while applying a suitable control program(software).

[0005] An initialization of the adjusting unit, which is configuredespecially as a hydrostatic unit, takes place with advantage. Here, thesubject matter is a hydraulic continuously variable transmission. Byinitializing the adjusting unit, it is possible, in the context of azero-point adaptation, to compensate possibly present tolerances and/orposition discrepancies of components operatively connected to theadjusting unit. This ensures a precise continuous adjustment of atransmission ratio on a continuously variable transmission by means ofthe adjusting unit.

[0006] Advantageously, the initialization takes place in the form of aparticular zero-point adaptation of the adjusting unit with reference toa forward travel and/or rearward travel of the vehicle. The adjustingunit has an operating position starting with which a reverse travel ofthe vehicle is possible, even though the planetary sets are configuredfor a forward travel. Here, one must distinguish between two separate,specific operating positions of the adjusting unit, namely, a firstoperating position starting with which a rearward travel of the motorvehicle is possible but not wanted and a second operating position,wherein a forward travel of the vehicle is possible and wanted. Thesetwo operating positions of the adjusting unit can shift because ofdeterioration of the adjusting unit and/or because of deterioration ofcomponents operatively connected to the adjusting unit. In this way,inaccuracies are compensated by means of the particular zero-pointadaptation of the adjusting unit with respect to a forward travel andrearward travel of the motor vehicle in a reliable manner. Theseinaccuracies are unwanted and go back to the particular positioning ofthe adjusting unit.

[0007] According to a preferred embodiment, the initialization takesplace before a particular taking into service of the motor vehicle.Because of the limited time span available for carrying out a correctinitialization, a relatively rapidly and precisely acting control isrequired, which can be ensured with the use of a higher-ranking shiftsequence control system for the coordinated and data-dependent controlof the gear stage switchover and of the continuous transmission ratioadjustment.

[0008] With advantage, the adjusting unit is adjusted by means of a stepmotor for the continuous adjustment of the transmission ratio. The stepmotor is operatively connected to the shift sequence control system. Astep motor can be controlled in a relatively simple manner and is suitedespecially for the displacement of the adjusting unit provided for thecontinuously changeable transmission ratio and configured especially asa hydrostatic unit. If present, occurring discrepancies between aparticular step motor position and a corresponding operating position ofthe adjusting unit (hydrostatic unit) can be compensated by means of theabove-mentioned initialization of the adjusting unit. Likewise, and inthe same manner, discrepancies between the desired and actual positionsof the step motor can be compensated. These discrepancies are, forexample, caused by electronic tolerances, fluctuations in a hydraulicpressure system or the like. Since the drive of the step motor isintegrated especially during a gear stage switchover in a phase controlof the shift sequence control, it is possible to trigger a step motoraction in each shifting phase.

[0009] Advantageously, the shift sequence control system determines anassumption of a defined shift position of the adjusting unit in advanceof enabling a gear stage switchover. In this way, it is ensured that theadjusting unit is, during a gear stage switchover (range change), in adefined shift position in which synchronism for the adjustment of gearsin the automatic transmission is present. These gears are represented bycorresponding planetary sets.

[0010] In accordance with a preferred embodiment, a position control ofthe adjusting unit takes place in the context of the continuoustransmission ratio adjustment. By means of a position control of thiskind, it is advantageously possible to compensate possibly presentdiscrepancies between a particular input value for a step motorposition, which is to be adjusted, and a corresponding position of theadjusting unit (hydrostatic unit). A model of characteristic values orcharacteristic fields or of mechanical or hydraulic basic informationcan be applied in the context of a position control to compensate forunwanted transmission ratio deviations.

[0011] Preferably, for position control, the following adjustingparameters are applied:

[0012] corrective step number per computation step;

[0013] output frequency of the corrective steps in a defined time span.

[0014] In this way, the transmission ratio can be influenced favorablywith respect to operation by means of the position control.

[0015] Further advantageous embodiments of the invention are evidentfrom the description.

DRAWINGS

[0016] The invention will be explained in greater detail in thefollowing in an embodiment with respect to the corresponding drawings.

[0017]FIG. 1 shows a sequence diagram of an initialization of anadjusting unit of a continuously variable automatic transmission; and,

[0018]FIG. 2 is a sequence diagram of adjusting or inputting atransmission ratio within a gear stage.

DESCRIPTION OF THE INVENTION

[0019] The method serves for the shift sequence control of a hydraulicautomatic transmission, especially of a motor vehicle having gear stageswitchover. The transmission ratio of the automatic transmission iscontinuously adjustable by means of an adjusting unit within a set gearstage (range). Here, it is provided that a coordinated, data-dependentcontrol of the gear-stage switchover and the continuous transmissionratio adjustment takes place by means of a common shift sequence controlsystem. The shift sequence control system fulfills the following threemain tasks:

[0020] initialization of the adjusting unit;

[0021] adjustment of the transmission ratio within a gear stage (range);

[0022] ensure a correct assumption of a defined shift position of theadjusting unit for a gear-stage switchover (change of range orshifting).

[0023]FIG. 1 shows a possible embodiment of an initialization of theadjusting unit in the form of a flowchart. A sequence start (start) isidentified by 10 and is connected to a branching 12 by means of a flowline 11. By means of the branching, the question is posed in the contextof an application adjustment variation as to whether reference should bemade to an absolute position of the adjusting unit. The adjusting unitcan be configured as a hydrostatic unit, which is operatively connectedto a controllable step motor for the continuous adjustment of thetransmission ratio of the automatic transmission. For the case that noreference to an absolute position of the adjusting unit should be taken,then a flow line 17 leads from the branching 12 to an operating unit 16by means of which a change of the step motor is initiated by X-steps. Inthe event that reference is to be made to an absolute position of theadjusting unit, a flow line 13 leads from the branching 12 to anoperating unit 14 which triggers a travel of the step motor to a stop,for example, to a lower stop. After completed positioning of the stepmotor, a flow line 15 leads from the operating unit 14 back to the flowline 17 and finally to the operating unit 16, which is connected bymeans of a flow line 18 to a branching 19. The branching 19 permits aninquiry with respect to a displacement of the hydrostatic unit(adjusting unit), that is, whether the adjustment leads to a higherspeed of the hydrostatic unit (flow line 40) or to a reducing or to nochange of the speed of the hydrostatic unit (flow line 20). The speed ofthe hydrostatic unit is determined, for example, by means of a sensor orby computation from other measured speeds.

[0024] In the case of a reducing (or not taking place) change of thespeed of the hydrostatic unit, a flow line 22 leads to an operating unit23, which initiates a change of the step motor by X-steps. The flow line22 is connected by means of a transition position 21 to the flow line20. A flow line 24 leads from the operating unit 23 to a branching 25 bymeans of which an inquiry is made as to whether a defined point P1(operating position of the adjusting unit, starting from which arearward travel of the motor vehicle is possible) or a defined point P2(operating position of the adjusting unit, starting from which a forwardtravel of the motor vehicle is possible) is reached. Should this notapply, a flow line 26 leads from a branching 25 back to the transitionposition 21. When the hydrostatic unit reaches the point P1 or P2, aflow line 27 leads, in contrast, from the branching 25 to a branching 28by means of which an inquiry is made as to whether the speed of thehydrostatic unit (adjusting unit) has remained constant or whether achange of this speed took place during the search for points P1 or P2.In the case of a speed change of the hydrostatic unit, a flow line 29leads from the branching 28 to a transition position 30 from which aflow line 31 leads to an operating unit 32 which initiates a change ofthe step motor by X-steps. For the case that no change of the speed ofthe hydrostatic unit took place, a flow line 49 leads to a transitionposition 48, which will be explained in greater detail hereinafter. Fromthe operating unit 32, a flow line 33 leads to a branching 34 by meansof which an inquiry takes place as to whether the step motor has reachedthe not-yet determined point P1 or P2. If the sought-for point has notbeen reached, a flow line 35 leads back to the branching 30. When thesought-for point P1 or P2 has been reached, a flow line 36 leads to anoperating unit 37 by means of which a positioning of the step motor tothe point P2 is initiated. A flow line 38, which starts from theoperating unit 37, leads to the sequence end 39 of the flowchart.

[0025] For the case that, according to the branching 19, an increasedspeed of the hydrostatic unit (adjusting unit) was determined, the flowline 40 leads to a transition position 41, from which a flow line 42leads to an operating unit 43, which initiates a change of the stepmotor by X-steps, that is, the displacement direction of the hydrostaticunit is reversed (adjusting direction reversed). The operating unit 43is connected by means of a flow line 44 to a branching 45 by means ofwhich an inquiry is made as to whether the hydrostatic unit has reachedthe point P1 or P2. For the case that none of these points has been set,a flow line 46 flows back to the transition position 41. If, incontrast, the hydrostatic unit has assumed one of these points, a flowline 47 leads to transition position 48 to which the flow line 49simultaneously leads from the branching 38. The transition position 48is connected by a flow line 50 to an operating unit 51 by means of whicha change of the step motor is initiated by X-steps, that is, if theoperating unit is reached via the flow lines 47 and 50, then thedisplacement direction of the hydrostatic unit is retained. If theoperating unit 51 is, however, reached via the flow lines (49, 50), thena reversal of the displacement direction of the hydrostatic unit takesplace. The operating unit 51 is connected by means of a flow line 52 toa branching 53, which permits an inquiry as to whether the step motorhas reached the point P1 or P2. If the sought-for point has not beenreached, a flow line 54 leads from the branching 53 back to thetransition position 48. In the event that the sought-for point has beenset, a flow line 55 leads from the branching 53 to the operating unit 37which, as mentioned above, initiates a positioning of the step motor toP2 and, by means of flow line 38, is connected to the sequence end 39 ofthe flowchart.

[0026] For the case that reference is to be made to an absolute positionof the adjusting unit (hydrostatic unit), the following sequence chainof the flowchart is run through: sequence start 10, flow line 11,branching 12, flow line 13, operating unit 14, flow line 15, flow line17, operating unit 16, flow line 18, branching 19, flow line 20,transition position 21, flow line 22, operating unit 23, flow line 24,branching 25, flow line 26 or flow line 27, branching 28, flow line 29,transition position 30, flow line 31, operating unit 32, flow line 33,branching 34, flow line 35 or flow line 36, operating unit 37, flow line38, sequence end 39.

[0027]FIG. 2 shows a flowchart for the continuous adjustment of atransmission ratio within a gear stage (range) of the automatictransmission. A transmission ratio suggestion is transmitted to theoperating unit 57 via a flow line 56. The operating unit 57 carries outa check of the above-mentioned suggestion as to its realizability. Aflow line 58 leads from the operating unit 57 to an operating unit 59 bymeans of which a conversion of the input data into an absolute stepposition of the step motor takes place. A flow line 61 leads from atransition position 60 provided on the flow line 58 to a furthertransition position 62 which is described in detail hereinafter. Theoperating unit 59 is connected by means of a flow line 64 to anoperating unit 65 which serves for the determination of a stepdifference to an old estimated step position of the step motor. For thispurpose, information with respect to an old estimated step position ofthe step motor is given via a flow line 66 to an operating unit 65. Theoperating unit 65 is connected additively to a transition position 77via a flow line 67. A flow line 78 leads from transition position 77 toan operating unit 79, which serves to limit the adjustment of the stepmotor to a maximum step number per computation cycle. A flow line 80leads from operating unit 79 to an operating unit 81, which supplies anoutput value for the adjustment of the step motor.

[0028] A further input quantity (actual value of the transmission ratio)is subtractively transmitted via a flow line 63 to the above-mentionedtransition position 62, from where a flow line 68 leads to an operatingunit 69, which serves for a model-like compensation of a transmissionratio deviation possibly present. A plurality of flow lines 70 lead tothe operating unit 69. By means of flow lines 70, data, for example withrespect to the particular output rpm present, oil temperature or thelike are given to the operating unit 69. From operating unit 69, a flowline 71 with the information “output frequency of the corrective stepsin a defined time duration” and a flow line 72 with information“corrective step number per computation step” lead to a switch 73. Theswitch 73 is clocked with the output frequency of the corrective steps.This means that, alternately, the value “corrective step number percomputation step” and a value of a function unit 74, which is connectedvia the flow line 75 to the switch 73, are supplied via the flow line 76to the transition position 77, while forming an additive logicoperation. Thereafter, and as mentioned above, by means of the operatingunit 79, a limiting takes place to maximum steps per computation cycleas well as the output of a corresponding adjusting value for the stepmotor by means of the operating unit 81.

[0029] The operating units 57, 59 and 65 of the sequence diagram of FIG.2 together with the corresponding flow lines conjointly form aprecontrol, while the operating unit 69 forms part of a positioncontrol. The position control functions to compensate possibly presentdiscrepancies between an input value for a step motor position, on theone hand, and an operation position of the hydrostatic unit (adjustingunit), on the other hand.

[0030] Advantageously, in each shift position of the automatictransmission, a step motor action for the continuous transmission ratioadjustment of the transmission can be triggered by a shift sequencecontrol system.

1. Method for shift sequence control of a continuous automatictransmission, especially of a motor vehicle, having gear-stageswitchover with the transmission ratio of the automatic transmissionbeing continuously adjustable within an adjusted gear stage by means ofan adjusting unit, characterized in that a coordinated, data-dependentcontrol of the gear-stage switchover and of the continuous transmissionratio adjustment takes place by means of a common shift sequence controlsystem.
 2. Method of claim 1, characterized in that an initialization ofthe adjusting unit takes place with the latter being configuredespecially as a hydrostatic unit.
 3. Method of one of the above claims,characterized in that the initialization takes place in the form of aparticular zero-point adaptation of the adjusting unit with respect to aforward travel and/or with respect to a rearward travel of the motorvehicle.
 4. Method of one of the above claims, characterized in that theinitialization takes place in advance of a particular taking intoservice of the motor vehicle.
 5. Method of one of the above claims,characterized in that the adjusting unit is adjusted by means of a stepmotor for the continuous transmission ratio adjustment, the step motorbeing operatively connected to the shift sequence control system. 6.Method of one of the above claims, characterized in that the shiftsequence control system determines the assumption of a defined shiftposition of the adjusting unit in advance of enabling a gear-stageswitchover.
 7. Method of one of the above claims, characterized in thata position control of the adjusting unit takes place in the context of acontinuous transmission ratio adjustment.
 8. Method of one of the aboveclaims, characterized in that the following adjusting parameters areapplied for the position control: corrective step number per computationstep; output frequency of the corrective steps in a defined time span.